A cutting tool comprised of a cemented carbide is provided. The cemented carbide is consisted of a composition including: a predetermined amount of at least one selected from specific carbide, nitride, and carbon nitride, except for cobalt and niobium; 0.01 to 0.08 mass % of oxygen; and the rest consisted of tungsten carbide and unavoidable impurities. The cemented carbide is further made up of a structure in which a tungsten carbide phase and a B1-type solid solution phase being expressed by M(CNO) or M(CO) where "M" is at least one selected from the group consisting of metals of the group IV, V, and VI in the periodic table, containing niobium as being essential, and containing oxygen at a rate of 1 to 4 atomic % are bound by a binder phase composed mainly of the cobalt. This achieves the cutting tool having a long tool life in high-speed interrupted cutting.